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L15 higher order chromatin
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L15 higher order chromatin

Created by
@TimeHonoredLimerick2759

Questions and Answers

During which phase does the cell replicate its DNA?

  • M phase
  • G2 phase
  • G1 phase
  • S phase (correct)

    • Chromosomes are always in an X shape during all phases of the cell cycle.

    False

    What are chromatid?

    Coiled 250nm fibers that make up chromosomes.

    During interphase, transcriptionally active regions are located near the ______ of the chromosome territory.

    <p>periphery</p> Signup and view all the answers

    Match the following phases of the cell cycle with their descriptions:

    <p>G1 phase = Cell growth and preparation for DNA synthesis S phase = DNA replication G2 phase = Preparation for mitosis M phase = Mitosis and cell division</p> Signup and view all the answers

    How many microns in diameter are chromosome territories typically?

    <p>1 to 2 microns</p> Signup and view all the answers

    Chromosomes occupy random regions within the nucleus.

    <p>False</p> Signup and view all the answers

    What is the role of DNA probes in studying chromosomes?

    <p>They bind specifically to each chromosome and display different colors.</p> Signup and view all the answers

    What is the primary role of enhancers in gene regulation?

    <p>To fine-tune gene expression</p> Signup and view all the answers

    Enhancers are always located directly upstream of the gene they regulate.

    <p>False</p> Signup and view all the answers

    What enzyme is mentioned as controlling gene transcription?

    <p>Histone modifying enzyme</p> Signup and view all the answers

    Some enhancers act upon their gene targets under __________ circumstances.

    <p>restricted</p> Signup and view all the answers

    Match the following terms with their descriptions:

    <p>Enhancer = A DNA sequence that enhances the transcription of a gene Promoter = A region that initiates gene transcription Exon = A coding sequence within a gene Intronic = A non-coding region within a gene</p> Signup and view all the answers

    How do enhancers fine-tune gene expression?

    <p>By altering chromatin structure</p> Signup and view all the answers

    There are hundreds of thousands of enhancers distributed across the genome.

    <p>True</p> Signup and view all the answers

    The organization of chromatin into the tightly condensed __________ and 'beads-on-a-string' structure is important for gene expression.

    <p>30-nm fibre</p> Signup and view all the answers

    What is one key feature that distinguishes enhancers from promoters?

    <p>Enhancers can function both upstream and downstream of a gene</p> Signup and view all the answers

    Enhancers always increase transcription regardless of their position relative to the gene.

    <p>True</p> Signup and view all the answers

    What are transcription factors that bind to enhancers called?

    <p>transcriptional activators</p> Signup and view all the answers

    Enhancers are typically composed of a cluster of transcription factor binding sites that work __________ to enhance transcription.

    <p>cooperatively</p> Signup and view all the answers

    Match the following terms with their definitions:

    <p>Enhancer = A DNA sequence that increases transcription Transcriptional activator = A protein that binds to enhancers to enhance transcription Histone tail acetylation = Modification that loosens chromatin structure H3K4me3 = An epigenetic mark associated with active transcription</p> Signup and view all the answers

    In which year were cellular enhancers first identified?

    <p>1983</p> Signup and view all the answers

    What epigenetic signatures are associated with enhancers?

    <p>histone tail acetylation and H3K4me3</p> Signup and view all the answers

    The process of enhancer function is independent of transcription factor binding sites.

    <p>False</p> Signup and view all the answers

    What do DNAseI hypersensitive sites correlate with?

    <p>Acetylation of histone tails</p> Signup and view all the answers

    Looser chromatin is more resistant to DNAse 1 than tighter chromatin.

    <p>False</p> Signup and view all the answers

    What is the function of the Locus Control Region (LCR) in relation to the β-globin gene locus?

    <p>It serves as a super enhancer to increase the rate of expression of the β-globin genes.</p> Signup and view all the answers

    The beta globin genes code for the beta chain of __________.

    <p>hemoglobin</p> Signup and view all the answers

    Which of the following features is associated with DNAseI hypersensitive sites?

    <p>Histone modification</p> Signup and view all the answers

    Genes can be activated or silenced based on developmental stage and age.

    <p>True</p> Signup and view all the answers

    What role do DNAse 1 hypersensitive sites play in chromatin structure?

    <p>They indicate regions of loose chromatin that are more accessible for gene activity.</p> Signup and view all the answers

    Match the following terms with their definitions:

    <p>DNAseI hypersensitive sites = Regions indicating accessible chromatin Locus Control Region = Super enhancer for gene expression Beta globin genes = Code for a component of hemoglobin Acetylation of histones = Modification associated with increased gene activity</p> Signup and view all the answers

    What is the role of enhancers in gene expression?

    <p>They can drive transcription in specific cell types.</p> Signup and view all the answers

    Silencers increase the rate of transcription from a gene promoter.

    <p>False</p> Signup and view all the answers

    What specific enhancer is noted for being active only in developing limb buds?

    <p>Limb bud-specific enhancer</p> Signup and view all the answers

    The Sonic hedgehog gene is regulated by different enhancers, which can induce expression in different _____ of tissue.

    <p>kinds</p> Signup and view all the answers

    Which gene is specifically mentioned in relation to enhancers and transcription regulation?

    <p>Sonic hedgehog</p> Signup and view all the answers

    Match the enhancers with their specific tissues:

    <p>Limb bud-specific enhancer = Limb buds Gut-specific enhancers = Gut Hindbrain-specific enhancers = Hindbrain Spinal cord enhancers = Spinal cord</p> Signup and view all the answers

    Different enhancers can induce the expression of the Sonic hedgehog gene in both the limb bud and hindbrain.

    <p>True</p> Signup and view all the answers

    What are the two different types of regulatory elements mentioned for controlling transcription?

    <p>Enhancers and silencers</p> Signup and view all the answers

    Study Notes

    Chromosome Compaction

    • Coiling of 250 nm fiber results in chromatid formation.
    • Chromatin consists of DNA and proteins, forming chromosomes mainly visible in X shape during mitosis.
    • Interphase is preparatory for mitosis, including G1 (growth), S (DNA replication), and G2 phases.
    • Chromosomes are decondensed during interphase and condense during mitosis.

    Chromosome Territories

    • Chromosomes occupy defined territories of 1 to 2 microns during interphase, with limited overlap at the borders.
    • Transcriptionally inactive regions are located in the territory's dense interior; active regions are more decondensed at the periphery.
    • Positioning of chromosomes in the nucleus is non-random; adjacent chromosomes risk translocations, often linked to cancer.

    Enhancers and Transcription Regulation

    • DNA probes with distinct fluorochromes identify each chromosome; enhancers were first identified in SV40 in 1981.
    • Enhancers are unique as they work in either orientation and can be positioned upstream or downstream of genes.
    • They significantly increase gene transcription and interact with transcription factors (TFs) which bind to specific motifs.
    • Enhancers often contain clusters of transcription factor binding sites, working cooperatively to boost transcription.

    Chromatin Structure and Gene Expression

    • Chromatin organization into 30-nm and 10-nm fibers determines gene expression sensitivity to DNase I.
    • Looser chromatin is more sensitive to DNase I, indicating active transcription regions with less nucleosome presence.
    • DNAse I hypersensitive sites correlate with histone tail acetylation, defining 'open' chromatin for gene activity.

    Locus Control Region (LCR)

    • The LCR acts as a super enhancer for the β-globin gene locus, leading to high expression levels necessary for hemoglobin production.
    • Contains DNAse I hypersensitive sites, indicating multiple enhancers' presence, which may be activated according to developmental stages.

    Sonic Hedgehog Gene Regulation

    • Sonic hedgehog (Shh) gene is regulated by long-range enhancers active in specific developmental contexts, such as limb buds.
    • Enhancers for Shh may be embedded within distant introns of other genes, influencing tissue-specific gene expression patterns.
    • Different enhancers correspond to varied developmental stages and cellular contexts, allowing precise regulation of gene transcription.

    Silencers

    • Silencers are DNA elements that reduce transcription rates at gene promoters, providing a mechanism to regulate gene expression downwards.

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    Description

    This quiz focuses on the intricate processes involved in the cell cycle, particularly during the M phase and interphase. Understand how chromatin compacts into chromosomes and the significance of the growth and preparation phases in cell division.

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